Industrial waste water containing dissolved hydrogen sulfide presents a significant pollution problem because of its high toxicity and unpleasant odor even at low concentrations. The treatment of such waste water is necessary before discharging it to the environment to reduce the hydrogen sulfide content to acceptable levels. The present invention provides a simple and effective method of removing of hydrogen sulfide from such waste water streams by the addition of non-chelated ferrous and/or ferric iron salts.
Typical sour water streams are those produced in oil refineries by water washing of sour liquid hydrocarbons and various cooler and condenser surfaces. Condensation of geothermal steam also produces sour water which requires treatment. Although the present invention may be used for the treatment of any sour water stream regardless of its source, the invention is of particular significance for treating geothermal condensates.
In a geothermal power plant geothermal steam is used to power a steam turbine which is connected to an electric power generator. The exhaust steam from the turbine is supplied to a condenser, and the resultant steam condensate is removed for reuse or discard. Geothermal steam, however, contains dissolved hydrogen sulfide in amounts which may range, for example, from as low as about 5 ppm to as high as about 1600 ppm and typically may average about 150 to 250 ppm. Dependent upon the type of condenser and its efficiency, a significant percentage, e.g., as much as 80%, of the hydrogen sulfide in the geothermal steam will end up as dissolved hydrogen sulfide in the condensate. This sour water stream must be treated to remove hydrogen sulfide in order to avoid environmental pollution.
U.S. Pat. No. 4,076,621 discloses a process for removing hydrogen sulfide from sour water by air stripping the dissolved hydrogen sulfide from the sour water and then scrubbing the air stream with an aqueous solution of chelated iron. U.S. Pat. Nos. 4,414,817; 4,451,442; and 4,468,929 disclose processes for removing hydrogen sulfide from geothermal steam or condensate using an aqueous solution containing at least the stoichiometric amount of a chelated polyvalent metal. U.S. Pat. No. 4,363,215 discloses a process for removing hydrogen sulfide from geothermal steam condensate using hydrogen peroxide and an iron chelate catalyst. U.S. Pat. Nos. 4,614,644 and 4,629,608 disclose processes for removing hydrogen sulfide from geothermal steam using a chelated iron solution and a cationic polymeric catalyst.
However, the known sour water treatment processes that rely on the use of chelated polyvalent metal solutions are complex and have other disadvantages, such as excessive consumption or discard of expensive chelating agent.